Dengue is a mosquito-borne viral infection that prevailed in some Asian and Latin American countries over the course of some recent past years.
Author: Muhammad Shoaib, University of Agriculture Faisalabad, Pakistan.
This viral infection causes severe illness and often leads to death in case of severe illness. According to some reports, (NCBI, 2008), in the last 50 years, the prevalence of this virus has increased with the approximation of 30 folds. And, at present, there are at least 100-400 million people are infected every year around the Globe (WHO, 2020).
Since 2000, the epidemic dengue has spread to new geographical regions and has increased in the areas where it was already present. In 2003, eight more countries, including Bangladesh, India, Pakistan and Maldives, reported the cases of dengue virus in their territories. Following this rapid increase and seriousness of the infection, in 2005, WHO activated their Global Outbreak Alert and Response Network (GOARN) to respond and take initiatives against this outbreak as in some areas, the fatality rate was recorded (3.55%) for some time, (NCBI, 2008). In 2011, Pakistan was heavily infected by dengue virus; especially Lahore was in more critical condition.
Scientific background of Dengue Virus:
The dengue virus is mostly written as DENV in most scientific readings, articles and books. It is a single-stranded RNA virus and is referred as positive-sense RNA because this virus can be directly and immediately translated into proteins. This virus belongs to the family Flaviviridae: genus Flavivirus. Five serotypes of this virus have been found. Dengue infections are caused by four closely related serotypes, namely DEN-1, DEN-2, DEN-3 and DEN-4. These variants of dengue virus are called serotypes because each type has a different type of interaction with antibodies present in human blood serum. In 1970, DEN-1 and DEN-2 variants of this virus were present in Central America and Africa, and all the four variants were present in Southeast Asia. By the end of 2004, all four types of the virus had been widely spread in different regions of the world. Now all four types of dengue viruses are present in tropical and subtropical regions of the whole world. (Beasley) (Nature).
Transmission of DENV:
Dengue virus is transmitted to humans via the bite of an infected mosquito. There are very few mosquito species that serve as a vector for the dengue virus. Here, a vector is an organism that itself does not cause disease but only carries and transmits the disease to the host organism. The most common vectors are arthropods, which are invertebrate animals. Arthropods include ticks, mites, fleas and mosquitoes etc. So, mosquitoes are the vectors for the dengue virus.
Another question that arises here is that, can any mosquito carry and transmit the dengue virus? And the answer is no as the dengue virus is mostly carried by the mosquitoes that are included in the genus Aedes. And in this genus too, the most common and primary vector is the mosquito Aedes aegypti. This particular specie of mosquito is the primary vector of Dengue and is responsible for the transmission and epidemics of Dengue. There are some other mosquito species that are included in the genus Aedes which can also transmit dengue virus to some extent. These species of the genus Aedes include Aedes albopictus, Aedes polynesiensis and Aedes scutillaris. (Nature)
Here, a detailed overview of Aedes aegypti is given as it is the primary vector for the transmission of dengue virus.
This particular mosquito, Aedes aegypti, is small and is dark in colour. This mosquito can be identified by the presence of white bands on its legs and a pattern of silver scales throughout its body. These mosquitoes dwell in the tropical and subtropical regions all over the world, mostly in the regions where winters are no colder than 10˚C. These mosquitoes require a moderately warm temperature for their survival. As these vectors are associated with the transmission of disease in humans, that is the reason they are mostly found near the houses and around densely populated areas. (Nature)
Life-cycle of Aedes Mosquito:
As all mosquitoes require water for the completion of their life cycle, Aedes aegypti also require water for carrying out its vital activities in its life cycle. Development of Aedes aegypti shows complete metamorphosis with four stages: egg, larva, pupa and adult. First three stages (egg, larva and pupa) can be seen in the water whereas, in the adult stage, the mosquito can fly freely in the air. The life span from egg to adult takes about one to six weeks, depending on the availability of food along with optimum temperature and humidity. Optimum or the most favorable temperature for its development is 28˚C with around 80% humidity.
Transmission of virus in Humans:
When a mosquito bites an infected person, the mosquito takes the blood of the infected person into its gut; in other words, the mosquito gets infected. The virus, which was present in the blood of the infected person, starts replicating in the gut of the mosquito and now when this mosquito bites a person, the person will get infected. Once the person gets infected after being bit by the infected mosquito, almost after four days, the person will develop viremia. Viremia is a condition when a person has a very high level of virus in its body. On the first day of viremia, the person may not show any symptoms of Dengue at all. Within five days of viremia, the person will start to show symptoms. (Nature)
Symptoms of the Disease:
The suspected persons may get fever up to 104˚F and, this fever is accompanied by 2 of the following symptoms mostly;
- Severe headache
- Swollen glands
- Muscle and joint aches
- Pain behind the eyes
The spread of Dengue can be reduced by taking serious account of some precautionary measures like;
- Using bed nets reduce the rate of spread by a large margin because when we use bed nets, the possibility of a mosquito to bite you reduces by a great deal.
- To avoid mosquito bite, one can use mosquito repellants that are available in the form of lotions. Use of aerosol insecticides, vaporizable mats and mosquito coils in the room is also very useful against the mosquitoes.
- Wearing a proper dress minimizes the exposed areas of your skin, and that reduces the probability of getting bit by the mosquitoes.
- Screening houses, offices and building is also effective against the spread of Dengue. One should not allow any water to stand in the house, office or building for a long period of time.
Vector control for Dengue:
There are a number of different methods being used to control the spread of Dengue. Commonly used control methods include;
- Chemical control: This method is frequently used to kill adult mosquitoes by the administration of insecticides in the form of aerosol sprays. And these insecticides should be used very carefully to avoid direct inhalation of spray or smoke.
- Biological control: To avoid the adverse effects of chemical agents, we can use a biological control method. In this method, different organisms are deliberately used to kill mosquitoes. Spiders, lizards and dragonflies are common predators of mosquitoes. Introduction of these animals can reduce the presence of mosquitoes to a certain degree.
- Horticulture management: This involves cutting of grass, weeds and shrubs where mosquitoes can find a place to hide.
More environmental friendly ways to control Dengue:
To make the control process of Dengue more environmental friendly, we can apply techniques which are environmental friendly and do not have any adverse effects. These environmental friendly methods include;
- Control at egg stage by the use of Ovitraps: We can use ovitraps to destroy the mosquito eggs. Ovitraps are a black container of plastic which are filled with water. There are small paddles that are present in the container that are in contact with the surface of the water. These ovitraps attract female mosquitoes to lay eggs in the water container. In these ovitraps, either the female mosquito is trapper, or the eggs are killed by mixing chemical in the water that is present in the ovitrap.
- Management for stagnant water: In proximity to human residences, Aedes aegypti breeds primarily in the water containers or stagnant water bodies. As the life cycle of Aedes mosquito is closely associated with the availability of water; therefore, we can apply better management techniques for controlling the spread of mosquitoes very effectively by not allowing water to stand for too long at a place or in a container.
- Using Integrated Disease Management: This is the method in which all the available techniques are used for combating a disease and participation of the community in the program is made ensured. By following this management technique, we can surely control Dengue by using Mass Media, Educational institutes and Mosques to make arrangements for awareness seminars so that each every person gets to know about the control of Dengue at very initial stage so that the deadly virus does not spread.
If we follow these methods very strictly, then we can definitely overcome the adverse effects of chemical agents that may affect the environment drastically.